Methods of manufacturing linearly expandable ureteral stents

ABSTRACT

A method includes forming an elongated member having a tubular shape. The elongated member includes a sidewall that defines a lumen. A spiral-shaped opening is formed in the sidewall such that the elongated member is configured to move between a retracted configuration and an expanded configuration along a longitudinal axis of the lumen. In some embodiments, the method further includes forming a distal retention structure. The distal retention structure can be disposed at a distal end of the elongated member and can define a lumen in fluid communication with the lumen defined by the sidewall of the elongated member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/628,304, entitled “Methods of Manufacturing Linearly ExpandableUreteral Stents”, filed Dec. 1, 2009 which is a divisional of U.S.patent application Ser. No. 12/241,450, entitled “Linearly ExpandableUreteral Stent,” filed Sep. 30, 2008, which is a divisional of U.S.patent application Ser. No. 10/283,873, entitled “Linearly ExpandableUreteral Stent,” filed Oct. 30, 2002, all of which are incorporatedherein by reference in their entirety.

BACKGROUND

The invention generally relates generally to medical devices for thedrainage of fluids, and more specifically to ureteral stents.

A ureter is a tubular passageway in a human body that conveys urine froma kidney to a bladder. The ureter begins with the renal pelvis and endsat the trigone region of the bladder, i.e., the triangulated areabetween both ureteral orifices and the bladder neck. Urine istransported through the ureter under the influence of hydrostaticpressure, assisted by contractions of muscles located within the walls(lining) of the ureter. Some patients experience a urological conditionknown as ureteral blockage or obstruction. Some common causes ofureteral blockage are the formation of tumors or abnormalities withinthe ureteral lining, or the formation and passage of kidney stones.

Ureteral stents are used to facilitate urinary drainage from the kidneysto the bladder in patients having a ureteral obstruction or injury, orto protect the integrity of the ureter in a variety of surgicalmanipulations. Stents may be used to treat or avoid ureter obstructions(such as ureteral stones or ureteral tumors) which disrupt the flow ofurine from the kidneys to the bladder. Serious obstructions may causeurine to back up into the kidneys, threatening renal function. Ureteralstents may also be used after endoscopic inspection of the ureter.

A stent may be uncomfortable to a patient because of intramural tunnelpain, imposed by the stent itself or in combination with intraoperativetrauma inflicted from device passage. Pain may also be caused by urinereflux back up the ureter during increased bladder pressure, e.g.,during voiding. Further, pain may stem from trigome irritation resultingfrom constant irritation, imposed by the bladder anchoring features orin combination with intraoperative trauma inflicted from device passage.Moreover, discomfort may arise from flank pain, caused by reflux orkidney anchoring.

Ureteral stents typically are tubular in shape, terminating in twoopposing ends: a kidney distal end and a bladder proximal end. Existingureteral stents compensate for the motion between the kidney and bladderby employing a pair of coil end-effectors, with one effector placed inthe bladder proximal end and the other in the kidney distal end. Asmotion occurs, the ureter slides up and down the stent body. Any othertravel results in an uncurling of the end effector(s).

SUMMARY

It is an objective of the invention to provide a patient, male orfemale, with a flexible device designed to maintain the patency of theureter and enable fluid drainage while minimizing the pains anddiscomfort commonly associate with an in-dwelling device.

Discomfort may be related to the stent rubbing against a wall of theureter, caused by the constant relative motion between the kidney andthe bladder. This motion may be as much as 5 centimeters (cm)(approximately 2 inches) and cycles with each breath of the patient.This is equal to approximately 17,000 cycles per day, assuming 1 breathevery 5 seconds. The present invention alleviates discomfort byproviding a stent that, like the ureter, linearly expands and contractsin response to relative motion between the kidney and the bladder,thereby reducing friction caused by a stent rubbing against a wall ofthe ureter.

In one aspect, the invention features a ureteral stent having anelongated member defining a lumen. The member has a solid sidewalldefining a spiral-shaped opening such that the member is linearlyexpandable along a longitudinal axis of the lumen. A distal retentionstructure is connected to a distal end of the elongated member forretention in a kidney, and a proximal retention structure is connectedto a proximal end of the elongated member for retention in a bladder.

One or more of the following features may also be included. The memberincludes a spring having a spring force of less than one pound. Themember includes a wire spring. The wire spring includes a metal alloy,that may include at least one of titanium, nickel, copper, cobalt,vanadium, and iron. The metal alloy includes nitinol. The wire spring iscoated with a polymer. The polymer includes at least one of urethane,nylon, thermoplastic polyurethane (TPU), thermoplastic polyesterelastomer, polyethyl, and silicone.

The stent has an elongated member including a tube having the solidsidewall and defining the lumen. The spiral-shaped opening is defined bya slit formed in the sidewall of the tube. The elongated member mayinclude a polymer, such as at least one of urethane, nylon, TPU,thermoplastic polyester elastomer, polyethyl, and silicone.

The elongated member includes an inner liner and an outer cover. A wirespring is sandwiched between the inner liner and the outer cover, withthe spiral-shaped opening being defined by slits formed in the innerliner and the outer cover, between a plurality of coils of the wirespring. The wire spring includes a metal alloy including, e.g., at leastone of titanium, nickel, copper, cobalt, vanadium, and iron. The metalalloy includes nitinol. At least one of the inner liner and the outercover includes a polymer. The polymer includes at least one of urethane,nylon, TPU, thermoplastic polyester elastomer, polyethyl, and silicone.

A removable introducer is sized for placement within the lumen.

In another aspect of the invention, a ureteral stent includes anelongated member defining a lumen, the member having a solid sidewallwith at least one slit formed therein such that the member is linearlyexpandable along a longitudinal axis of the lumen. A distal retentionstructure is connected to a distal end of the elongated member forretention in a kidney, and a proximal retention structure is connectedto a proximal end of the elongated member for retention in a bladder.

In yet another aspect of the invention, a method of facilitating urinarydrainage from a kidney to a bladder in a patient that reduces discomfortto the patient includes positioning a ureteral stent in a ureter of apatient, the ureteral stent having an elongated member defining a lumen,the member having a solid sidewall defining a spiral-shaped opening suchthat the member is linearly expandable along a longitudinal axis of thelumen, a distal retention structure connected to a distal end of theelongated member for retention in the kidney, and a proximal retentionstructure connected to a proximal end of the elongated member forretention in the bladder. The elongated member is allowed to linearlyexpand and contract between an expanded position and a retractedposition, based on at least one of: relative positioning of organswithin the patient, a breathing pattern of the patient, and relativepositions of the kidney and the bladder. In addition, the elongatedmember can be biased to the retracted position.

In yet another aspect of the invention, a method of manufacturing alinearly expandable ureteral stent includes providing an elongatedmember defining a lumen, the member having a solid sidewall defining aspiral-shaped opening such that the member is linearly expandable alonga longitudinal axis of the lumen. The stent also includes a distalretention structure and a proximal retention structure. The distalretention structure is connected to a distal end of the elongatedmember, and the proximal retention structure is connected to a proximalend of the elongated member.

The following features may be included. Providing the elongated memberincludes providing a wire spring. Providing the wire spring includescoating the wire spring with a polymer. Providing the wire springincludes sandwiching the wire spring between an inner lining and anouter cover. The inner lining and outer cover include extruded sheets.The inner lining and outer cover are shrunk, and slits are formedthrough the inner lining and outer cover between a plurality of coils ofthe wire spring. The inner lining and the outer cover are melted, andslits are formed through the inner lining and outer cover between aplurality of coils of the wire spring. The elongated member is providedby forming a tube including a polymer, and forming a spiral slit throughthe tube.

In yet another aspect of the invention, a method of placing a ureteralstent in a patient includes providing a ureteral stent. The ureteralstent includes an elongated member defining a lumen, the member having asolid sidewall defining a spiral-shaped opening such that the member islinearly expandable along a longitudinal axis of the lumen. The ureteralstent also includes a distal retention structure connected to a distalend of the elongated member, and a proximal retention structureconnected to a proximal end of the elongated member. The ureteral stentis inserted into a ureter of the patient. The ureteral stent ispositioned in the patient with the distal retention structuresubstantially within the kidney of the patient, the elongated membersubstantially within the intramural tunnel portion of the ureter, andthe proximal retention structure substantially within the bladder of thepatient. In a detailed embodiment, the ureteral stent can furtherinclude a removable introducer sized to fit within the lumen andinserting the ureteral stent includes inserting the stent with theremovable introducer into the ureter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention.

FIG. 1A is a schematic view of a human urinary tract, illustrating theplacement of one embodiment of the invention within the ureter of apatient, in an expanded position;

FIGS. 1B-1C are detailed sectional views of a portion of the embodimentof the invention of FIG. 1A;

FIGS. 2A-2B are schematic representations of the embodiment of theinvention illustrated in FIGS. 1A-1C in a retracted position;

FIGS. 3A-3B are schematic representations of another embodiment of theinvention in an expanded position;

FIGS. 4A-4C are schematic representations of the embodiment of theinvention illustrated in FIGS. 3A-3B in a retracted position;

FIGS. 5A-5C are schematic representations of yet another embodiment ofthe invention at various stages of fabrication;

FIGS. 6A-6C are schematic representations of yet another embodiment ofthe invention in retracted and expanded positions; and

FIG. 7 is a schematic representation of an introducer.

DETAILED DESCRIPTION

The invention features temporary ureteral stents that, when positionedwithin the ureter of a patient, significantly reduce discomfort to thepatient. As used herein, proximal refers to the end of a stent closestto a medical professional when placing a stent in a patient. As usedherein, distal refers to the end of a stent furthest from a medicalprofessional when placing a stent in a patient.

Referring to FIG. 1A, a human urinary tract 100 includes a ureter 105that transports urine from a kidney 110 to a bladder 115. When ureter105 becomes blocked or obstructed due to, for example, post-kidney stonefragmentation/removal and ureteral stricture therapy, fluid drainage canbecome restricted. Ureteral stents are medical devices that areimplanted within ureter 105 to restore patency and fluid drainage. Aureteral stent 120 is located within the ureter 105 of a patient, with adistal retention structure 125 in a pelvis 130 of kidney 110, and aproximal retention structure 135 in the bladder 115, proximate ureteralorifice 136. A lumen 137 extends within distal retention structure 25,an elongated member 140, and proximal retention structure 135 to providefor the passage of fluid. Distal retention structure 125 is connected toa distal end 142 of elongated member 120, and proximal retentionstructure 135 is connected to a proximal end 144 of elongated member140. Distal retention structure 125 secures distal end 142 of elongatedmember in or proximate to kidney 110. Proximal retention structure 135secures proximal end 144 of elongated member 140 in or proximate bladder115, as well as facilitates the removal of stent 120 by providing a loopsuitable for grasping by a hook.

Distal retention structure 125 and proximal retention structure 135 canbe fabricated of materials such as nylon, polyurethane, or the like.Heat bonding of these materials to elongated member 140 is convenientlyaccomplished by, for example, using an RF heat source as is commonlyemployed for plastic tubes and catheters. The desired shape of distaland proximal retention structures 125, 135 can be formed by injectionmolding or extrusion. They can also be heat-formed, for example, byflaring the working piece over an anvil of an appropriate shape, withthe application of heat. The shape of distal retention structure 125 canbe, for example, a coil, a pig-tail coil, J-shaped, or a helical coil.The shape of proximal retention structure 135 can be, for example, acoil, a pig-tail coil, J-shaped or a helical coil. In the illustratedembodiment, both distal and proximal retention structures 125, 135 areJ-shaped.

Referring to FIGS. 1A-1C, elongated member 140 includes a tube 145having a solid sidewall 150. A slit 155 is formed in sidewall 150,defining a spiral-shaped opening 160, so that elongated member 140 islinearly expandable along a longitudinal axis 165 of lumen 137.Elongated member 140 can be formed from a polymer, such as, e.g.,urethane, nylon, TPU, thermoplastic polyester elastomer, polyethyl, andsilicone.

Elongated member 140 can be manufactured by, for example, injectionmolding or extrusion and optionally a combination of subsequentmachining operations. Extrusion processes, for example, can be used toprovide a uniform shape, such as a single monolithic tube. Spiral-shapedopening 160 can be created in the desired locations by a subsequentmachining operation.

Referring also to FIGS. 2A and 2B, elongated member 140 is linearlyexpandable between an expanded position (see, e.g., FIGS. 1A-1B) and aretracted position (see FIGS. 2A-2B). When elongated member 140 isretracted, spiral-shaped opening 160 is closed. A difference in anexpanded length L.sub.1 of elongated member 140 in its expanded positionand a retracted length L.sub.2 of elongated member 140 in its retractedposition can be approximately 5 cm (approximately 2 inches). Forexample, elongated member 140 can be sized so that refracted lengthL.sub.2 is approximately 8 cm to 30 cm, and expanded length L.sub.1 isapproximately 13 cm to 35 cm. Elongated member 140 can have, in itsretracted position, an outer diameter d.sub.1 corresponding toapproximately 3.7 French to 14.0 French. Lumen 137 can have a diameterd.sub.2 when elongated member 140 is in its retracted position, to allowthe introduction of a guide wire.

In use, elongated member 140 can expand linearly up to 2 inches toexpanded length L.sub.1, to provide comfort to the patient bycompensating for at least one of: relative positioning of organs withinthe patient, a breathing pattern of the patient, and relative positionsof kidney 110 and bladder 115. Because of the possibility of linearexpansion, a physician may be able to select ureteral stent 120 with asmaller size than would be required with a conventional stent.

Referring to FIGS. 3A-3B, in another embodiment, ureteral stent 300 hasan elongated member 310 including a spring 315. Distal retentionstructure 125 is connected to a distal end 312 of elongated member 310,and proximal retention structure 135 is connected to a proximal end 314of elongated member 310.

Spring 315 has a plurality of coils 320 having, in some embodiments, aspring force less than one pound. Spring 315 includes a wire 325 formedfrom a superelastic material. Materials with superelastic propertiesmake it possible to configure a component into a particular shape, suchas a coil or a sleeve, and then modify reversibly the geometry of thecomponent, such as by straightening it out. Once the device isstraightened, after removal of the straightening force, the componentreverts spontaneously to its predetermined configuration, therebyregaining its former geometry. In so doing, the component provides abiasing force back to its original configuration.

Superelastic materials can include alloys of In—Ti, Fe—Mn, Ni—Ti, Ag—Cd,Au—Cd, Au—Cu, Cu—Al—Ni, Cu—Au—Zn, Cu—Zn—Al, Cu—Zn—Sn, Cu—Zn—Xe,Fe.sub.3Be, Fe.sub.3Pt, Ni—Ti—V, Fe—Ni—Ti—Co, and Cu—Sn. Preferably,wire 325 includes a superelastic material comprising a nickel andtitanium alloy, known commonly as nitinol, available from Memory Corp.of Brookfield, Conn. or SMA Inc. of San Jose, Calif. The ratio of nickeland titanium in nitinol can be varied. Examples include a ratio of about50% to about 52% nickel by weight, or a ratio of about 48% to about 50%titanium by weight. Nitinol has shape retention properties in itssuperelastic phase.

Wire 325 can have a coating 330 including a biocompatible material, suchas a polymer like urethane, nylon, TPU, thermoplastic polyesterelastomer, polyethyl, or silicone. Coating 330 can be applied to wire325 by various methods, such as spray coating or painting.

Ureteral stent 300 has an expanded position (see, e.g., FIGS. 3A-3B) anda retracted position (see, e.g., FIGS. 4A-4C). In the retractedposition, coils 320 abut each other, defining a lumen 332 that issubstantially enclosed. In the expanded position, coils 320 define aspiral-shaped opening 335, formed by a plurality of gaps 340 betweencoils 320. Elongated member 310 is linearly expandable along alongitudinal axis 345 of lumen 332.

Referring to FIGS. 5A-5C, in another embodiment, a stent 500 is formedby placing a wire spring 510, having a plurality of coils 512, betweenan inner lining 515 and an outer cover 520. Wire spring 510 can be madefrom a metal alloy including, for example, titanium, nickel, copper,cobalt, vanadium, or iron. The metal alloy can include nitinol, amaterial including nickel and titanium. Inner lining 515 and outer cover520 can each be formed from an extruded sheet Inner lining 515 and outercover 520 can each be made from a polymer, such as urethane, nylon, TPU,thermoplastic polyester elastomer, polyethyl, and silicone.

Inner lining 515 and outer cover 520 are deformed at elevatedtemperatures to fully surround wire spring 510. For example, innerlining 515 and outer cover 520 can be shrunk by, e.g., exposure to aheat lamp. Alternatively, inner lining 515 and outer cover 520 can bemelted by, e.g., heating in an oven. After deformation, a plurality ofslits 525 are formed through inner lining 515 and outer cover 520between coils 512 to form an elongated member 530. Elongated member 530is linearly expandable along a longitudinal axis 535 of a lumen 540extending through elongated member 530. Elongated member 530 isconnected at a distal end 545 to a distal retention structure 125, andat a proximal end 555 to a proximal retention structure 135.

Referring to FIGS. 6A-6C, in yet another embodiment, a stent 600 has anelongated member 610 connected to distal retention structure 125 forretention in a kidney and proximal retention structure 135 for retentionin a bladder. Elongated member 610 defines a lumen 620, and has a solidsidewall 625. Solid sidewall 625 can be made of a biocompatiblematerial, such as a polymer, e.g., urethane, nylon, TPU, thermoplasticpolyester elastomer, polyethyl, or silicone. Solid sidewall 625 has atleast one slit 630 formed in it, so that elongated member 610 islinearly expandable along a longitudinal axis 635 of lumen 620.

Referring to FIG. 7, in another aspect, the invention provides anapparatus for delivering a stent into a patient. An introducer 700includes a guide wire 710. A proximal end 720 of guide wire 710 includesa grip 725 to assist in using the device.

Referring to FIG. 7 and also to FIG. 1A, in use, a stent, (e.g., stent120) is mounted on introducer 700. Distal retention structure 125 isthreaded over guide wire 710, and most of its inherent curvature isremoved. Next, the guide wire 710 is inserted into bladder 115 throughureteral orifice 136 up ureter 105, and into kidney 110. A pusher (notshown) is then moved along guide wire 710, pushing stent 120 along guidewire 710 towards kidney 110. Proximal end 144 of elongated member 140can be positioned either at or distal to ureteral orifice 136. Stent 120can also be positioned such that proximal retention structure 135 is ator distal to ureteral orifice 136.

Once the surgeon has achieved the desired positioning of stent 120,guide wire 710 is removed, while holding the pusher stationary tomaintain stent 120 in position. Finally, the pusher is removed fromwithin the patient, leaving stent 120 in place. Using this method, thestent of the invention can be precisely positioned within ureter 105 ofthe patient. The method can also be used to accurately position proximalretention structure 135 in bladder 115, and distal retention structure125 within kidney 110.

In one embodiment of the invention, the guide wire, pusher, and stentare inserted into ureter 105 percutaneously through a surgical opening.In another embodiment, they are inserted into the ureter via the urinarytract of the patient.

While the invention has been particularly shown and described withreference to specific preferred embodiments, it should be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. A method for forming a ureteral stent comprising: disposing a wirebetween an inner lining and an outer cover; heating the inner lining andthe outer cover such that the inner lining and the outer cover surroundthe wire to form an elongated member; and forming a continuousspiral-shaped opening in the elongated member such that the elongatedmember is configured to move between a retracted configuration and anexpanded configuration along a longitudinal axis elongated member. 2.The method of claim 1, further comprising: forming a distal retentionstructure, the distal retention structure being disposed at a distal endof the elongated member.
 3. The method of claim 2, wherein the formingthe distal retention structure includes forming the distal retentionstructure via at least one of injection molding, extrusion andheat-formed.
 4. The method of claim 2, wherein the forming the distalretention structure includes forming the distal retention structure tohave a shape selected from a group consisting of a “J” shape, a coilshape, a pig-tail coil shape and a helical coil shape.
 5. The method ofclaim 1, further comprising: forming a proximal retention structure, theproximal retention structure being disposed at a proximal end of theelongated member.
 6. The method of claim 1, wherein the forming acontinuous spiral-shaped opening includes forming a continuousspiral-shaped opening that includes a plurality of revolutions aroundthe elongated member.
 7. The method of claim 1, further comprising:forming a retention structure; and bonding the retention structure to anend portion of the elongated member.
 8. The method of claim 1, furthercomprising: forming a first retention structure; bonding the firstretention structure to a first end portion of the elongate member;forming a second retention structure; and bonding the second retentionstructure to a second end portion of the elongate member.
 9. The methodof claim 1, wherein the heating includes exposing the inner lining andthe outer cover to a heat lamp.
 10. The method of claim 1, wherein theheating includes placing the wire disposed between the inner lining andthe outer cover in an oven.
 11. A method for forming a ureteral stentcomprising: disposing a wire between an inner lining and an outer cover;heating the inner lining and the outer cover such that the inner liningand the outer cover surround the wire to form an elongated member;forming a first slit in the elongated member, the first slit configuredto define a first rotation of a continuous spiral-shaped opening; andforming a second slit in elongated member, the second slit configured todefine a second rotation of the continuous spiral-shaped opening. 12.The method of claim 11, further comprising: forming a distal retentionstructure, the distal retention structure being disposed at a distal endof the elongated member.
 13. The method of claim 12, wherein the formingthe distal retention structure includes forming the distal retentionstructure via at least one of injection molding, extrusion andheat-formed.
 14. The method of claim 12, wherein the forming the distalretention structure includes forming the distal retention structure tohave a shape selected from a group consisting of a “J” shape, a coilshape, a pig-tail coil shape and a helical coil shape.
 15. The method ofclaim 11, further comprising: forming a proximal retention structure,the proximal retention structure being disposed at a proximal end of theelongated member.
 16. The method of claim 11, further comprising:forming a retention structure; and bonding the retention structure to anend portion of the elongated member.
 17. The method of claim 11, furthercomprising: forming a first retention structure; bonding the firstretention structure to a first end portion of the elongate member;forming a second retention structure; and bonding the second retentionstructure to a second end portion of the elongate member.
 18. The methodof claim 11, wherein the heating includes exposing the inner lining andthe outer cover to a heat lamp.
 19. The method of claim 11, wherein theheating includes placing the wire disposed between the inner lining andthe outer cover in an oven.